MUSR studies of spin excitations in polyaniline

Abstract

Summary form only given. Muon techniques have been used to study muon-generated and dopant-generated spin excitations in polyaniline. For non-metallic emeraldine (EB) and pernigraniline (PPG), it is found that both mobile and bound spins are present. The hyperfine coupling between the muon and the unpaired electron is extracted from the field dependent longitudinal muon polarisation. It is independent of temperature for (EB), but falls by a factor of /spl ap/2 between 300K and 15K for PPG. This indicates an increased spin delocalisation for PPG which may be associated with the mobile solitons predicted for PPG. Relaxation rate studies provide information about the spin dynamics: 1D spin diffusion is observed at low temperature for both materials with a crossover to 2 or 3D behaviour at higher temperature. In metallic polyaniline, in contrast to the undoped cases, the relaxation is rapidly quenched by field at all temperatures. At low temperatures a marked difference between low and high field behaviour is seen, with a crossover point around 40G. This critical field gives a cutoff frequency which is related to the on-chain diffusion rate in the doped material. The cutoff frequency is found to be quite constant between I 00 K and 20 K at /spl sim/-0. 5 MHz.